Several patents, patent applications and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains. The entire disclosure of each of these patents, patent applications and publications is incorporated by reference herein.
Laminated safety glazing has been in use for almost a century. It has been used in a variety of industries, such as the architecture and transportation industries. For example, laminated safety glazing that possesses high impact and penetration resistance and that does not scatter glass shards or debris when it is shattered can be used as windows in buildings and as windshields or moon roofs in automobiles.
Laminated safety glazing is typically formed by bonding two glass sheets together with a polymeric interlayer sheet. In some cases, one or both of the glass sheets may be replaced with optically clear rigid polymeric sheets, such as polycarbonate sheets.
The polymer interlayer sheets used in safety glazing are typically made from relatively thick polymer sheets that have adequate toughness and are bonded to the glass sheets. Thus, in the event of a crack or crash, objects do not penetrate the safety glazing and glass shards adhere to the interlayer. Widely used interlayer materials include poly(vinyl acetal) (e.g., poly(vinyl butyral) (PVB)), poly(urethane) (PU), poly(ethylene vinyl acetate) (EVA) and ethylene acid copolymers.
Ionomers of ethylene acid copolymers have also been used as interlayer sheets in safety glazing. See, e.g., U.S. Pat. Nos. 3,344,014; 3,762,988; 4,663,228; 4,668,574; 4,799,346; 5,759,698; 5,763,062; 5,895,721; 6,150,028; 6,265,054; and 6,432,522; U.S. Patent Publication Nos. 20020155302; 20020155302; 20060182983; 20070092706; 20070122633; 20070289693; 20080044666; and PCT Patent Publication Nos. WO9958334; WO2006057771; and WO2007149082.
Because of a generally increasing desire for protection from crime, safety glazing with ballistic resistance is now in higher demand. Such ballistic resistant safety glazing generally comprises two distinct zones, an impact zone and an anti-spall zone. The impact zone is the part that is closer to the impact force. It is designed to possess high impact resistance and is often formed of multiple layers or plies of glass interspaced by polymer sheets. The anti-spall zone is the part that is farther away from the impact force. It is designed to prevent splinters from detaching upon impact and is often formed of a glass or film layer. In some structures, the anti-spall zone may further include an energy absorbing polymer sheet layer which may also provide additional bonding force between the impact and anti-spall zones. Safety glazing with ballistic resistance can be used as armors for civilian cars, military vehicles, cash trucks, armored cars, and the like. In addition, they may also be used on buildings, high speed trains, aircraft, construction equipment, farm equipment, and the like. See, e.g., U.S. Pat. Nos. 5,906,411 and 6,276,750.
Various transparent safety glazings with ballistic resistance have been described in, for example, U.S. Pat. Nos. 2,991,209; 3,624,238; 3,657,057; 3,671,370; 3,917,891; 3,930,452; 4,125,669; 4,130,684; 4,204,026; 4,322,476; 4,328,277; 4,355,077; 4,594,290; 4,595,624; 4,647,493; 4,747,896; 4,774,143; 4,812,359; 4,861,666; 4,879,183; 5,019,443; 5,229,204; 5,318,853; 5,496,643; 5,506,051; 5,747,170; 6,108,999; 6,129,974; 6,280,826; 6,327,954; 6,334,382; 6,569,787; 6,818,268; and 7,191,694 and US Patent Publication Nos. 20010032540 and 20050238880.
In particular, U.S. Pat. No. 5,002,820 describes an anti-spalling safety glazing including a front lamina formed of polycarbonate or glass sheet(s) and a back lamina formed of an ionomer sheet and a 0.3 to 1.8 mm thick glass sheet. In addition, PCT Patent Publication No. WO03068501 describes a bullet-resistant glazing including an impact zone formed of multiple plies of glass sheets interspaced by PVB sheets and an anti-spall zone formed of an ionomer sheet and a chemically strengthened thin glass sheet.
Examples of descriptions of the use of plastic films in ballistic resistant safety glazing include, e.g., U.S. Pat. Nos. 4,072,779; 4,075,386; 4,112,171; 4,242,403; 4,469,743; 4,952,457; 4,956,227; 5,368,904; 5,393,365; 5,415,942; 5,501,910; 5,560,149; 5,567,529; 5,631,089; 5,645,940; 5,698,053; 5,707,695; 5,858,483; 5,908,674; 6,630,235; and 7,294,401 and U.S. Patent Publication No. 20040111986). In particular, U.S. Pat. No. 5,567,529 describes an anti-bullet glazing comprising an anti-spall zone formed of a composite of a PVB sheet and a poly(ethylene terephthalate) (PET) film. U.S. Patent Publication No. 20020160198 describes bullet-proof glass screen comprising a fracture-proof plastic film (i.e., a polyethylene, polyester, poly(vinyl chloride), or polycarbonate film) as the innermost surface that faces to the protected object.
One way to improve ballistic resistance of a safety glazing is to increase the number of laminate layers or the thickness of the laminate layers, especially in the impact zone. Consequently, as the total thickness of the glazing increases, the total weight of the glazing goes up and the transparency of the glazing goes down. These effects are plainly undesirable. Accordingly, there remains a need for thin or light-weight transparent safety glazing with ballistic resistance.